Puget Sound Energy, which serves more than a million customers in 11 counties, is a target of the Sierra Club’s Beyond Coal campaign.

Despite the utility’s profile as a leader in the development of wind farms and other clean energy, it still gets about 35% of its power from coal-fired power plants, chief among them, the Colstrip Generating Station in eastern Montana.

“It’s an old, very, very dirty pant – the biggest source of climate pollution in the western United States,”says Josh Nelson is with CREDO Action, which has joined forces with the Sierra Club on this issue. “The pollution from this plant has been making local residents sick for decades. And it even affects air quality as far away as Yellowstone National Park.”

He says they now have more than 5,000 signatures on a petition demanding an end to the utility’s reliance on coal.

Puget Sound Energy says Colstrip has been updated since its construction in the 1970s and '80s and is now actually one of the cleanest coal-fired power generators in the U.S. Its size is what makes it such a big polluter.

PSE spokesman Grant Ringel says coal is still part of the utility’s portfolio because it’s reliable and affordable. It costs about half as much as any other energy source out there.